# Test Weights

NOTE 9: To sort out a group of shafts a test weight is usually used. The device typically weighs about 200 grams in order to simulate the weight of a driver head. A Craftsman 3/8" drill chuck # 20986 is ideal for this purpose. It typically costs about $15. With shafts checked before the clubs are built up, small adjustments in the tipping can result in a set matched to a cpm or two with little difficulty assuming the original shafts are reasonably close to one another (a few cycles). When testing a set of raw iron shafts I screw a bolt into the back end of the chuck to up the weight to that of a 3 iron to make it a more realistic.

One note of caution; A 200 gram test weight and a 200 gram driver head will not produce the same frequency. This is simply due the fact that the center of gravity of the driver head is further from the shaft tip than the test weight. The cg of the chuck is just about aligned with the tip of the shaft. A driver can have a cg as much as on inch beyond the tip. This effectively makes the driver one inch longer. I supply a 205 gram test weight (the weight is adjustable) that has a cg which is consistent with a club head for $20.

As an experiment I measure a shaft with a test weight at 255 cpm. A driver head with the identical weight of the chuck measured 250 cpm. I carefully measured the difference in their centers of gravity and got .55". (It was a through bore) From the equation of Tech Note 1, variation of frequency should be the ratio of the square root of the cubes of the shaft lengths. The length of the cantilever beam, the amount hanging out of the clamp was about 40 inches. If we the ratio the square root of the cubes of 40.55 and 40 we get: 1.0207. The ratio of 255 cpm to 250 cpm is 1.0200. Pretty close.